1. Field of the Invention
The present invention relates to a clock spring for use with a steering device of an automobile, for example, including a fixed member, a movable member, and a cable for effecting electrical connection between the fixed member and the movable member.
2. Description of Related Art
A clock spring is generally constructed of a fixed member, a movable member rotatably mounted on the fixed member, a flexible cable connecting the fixed member and the movable member. Such a clock spring is used as an electrical connecting device for effecting electrical connection between the fixed member and the movable member adapted to be rotated with a finite number of revolutions as in a steering device of an automobile.
In a known clock spring of this kind, a cable accommodating portion is defined between the fixed member and the movable member, and a flat cable formed by laminating a pair of strip films with a plurality of conductors sandwiched therebetween is loosely accommodated in the cable accommodating portion under a spirally wrapped condition. One end of the flat cable is fixed to an outer cylindrical portion formed on either the fixed member or the movable member, while the other end of the flat cable is fixed to an inner cylindrical portion formed on the other of the fixed member and the movable member.
When the movable member of the clock spring is rotated, the flat cable accommodated in the cable accommodating portion can be wrapped onto the inner cylindrical portion from the outer cylindrical portion or unwrapped from the inner cylindrical portion to the outer cylindrical portion according to a rotational direction of the movable member. Accordingly, while the flat cable is being unwrapped from the inner cylindrical portion to the outer cylindrical portion, almost no tension is applied to the flat cable, and electrical connection between the fixed member and the movable member rotating relative thereto can be maintained at all times.
In the above-mentioned conventional clock spring, it is known that a positioning mechanism is provided between the fixed member and the movable member, which mechanism has a position indicating portion changing with a rotational amount of the movable member. This positioning mechanism is visually observed from the outside of the clock spring by an operator, so that a wrapped condition of the flat cable accommodated in the cable accommodating portion defined between the fixed member and the movable member can be confirmed by the operator. However, although such a positioning mechanism is provided, it is difficult to completely eliminate a problem that the clock spring is erroneously mounted in a steering device or the like under the condition where the movable member is rotationally offset in either a clockwise or counterclockwise direction from a neutral position.
It is assumed that the clock spring is erroneously mounted under the condition where a rotatable amount of the movable member in a wrapping direction of the flat cable is smaller than a predetermined amount. In this case, when the movable member is rotated in the wrapping direction of the flat cable by an amount larger than the predetermined amount, a tension is applied to the flat cable to thereby forcibly cut the flat cable. The cutting of the flat cable is electrically detected to find the erroneous mounting of the clock spring. However, the flat cable is very hard to cut as is well known, and it is accordingly necessary to provide a cutter or the like for cutting the flat cable in the clock spring, thus complicating the internal construction of the clock spring.
In contrast, it is assumed that the clock spring is erroneously mounted under the condition where a rotatable amount of the movable member in an unwrapping direction of the flat cable is smaller than the predetermined amount. In this case, when the movable member is rotated in the unwrapping direction of the flat cable by an amount larger than the predetermined amount, the flat cable is inverted in the vicinity of an inner circumferential end thereof. Thus, excess rotation of the movable member is not hindered. It is therefore impossible to forcibly cut the flat cable so as to detect the erroneous mounting of the clock spring.